Arrays and Sorting: Selection Sort (C Program/Java Program source code, a tutorial and an MCQ Quiz on Sorting)

To go through the C program / source-code, scroll down to the end of this page

Selection Sort

The idea of the selection sort is to find the smallest element in the list and exchange it with the element in the first position. Then, find the second smallest element and exchange it with the element in the second position, and so on until the entire array is sorted.

Algorithm:

For every index from 0 to number_of_elements-1, we find the element which is appropriate for that index and we swap the element which is already there with the element which has to be there. Finding the element which is appropriate for an index is simple. We just have to find the minimum value which is there from that index till number_of_elements-1.

1. minIndex denotes the index which has the minimum value which for now assumed to be

the value at current index and we update it in a for loop.

2. For elements from minIndex+1 to the last element of the list check if some index has got

element smaller than minimum then update minindex to be that index.

3. Then swap the two elements i.e. the element at minidex in 1 and the element at the

updated minindex.

4. Follow the first three steps for every index from 0 to number_of_elements-1.

To Check out a Java Applet Visualization of Selection Sort, click on the image below :

The gadget spec URL could not be found

Properties:

Best case performance – When the list is already sorted O(n2).

Worst case performance - When the list is sorted in reverse order O(n2).

Average case performance – O(n2).

It does not require any extra space for sorting, hence O(1) extra space.

It is not stable.

O(n2) time complexity makes it difficult for long lists.

Tutorial :

Selection Sort - C Program Source Code

#include<stdio.h>/* Logic : For every index from 0 to number_of_elements-1, we find the element which is appropriate for that index and we swap the element which is already there with the element which has to be there. Finding the element which is appropriate for an index is simple. We just have to find the minimum value which is there from that index till number_of_elements-1. */voidSelectionSort(int*array,int number_of_elements){int iter,jter,minIndex,temp;for(iter =0;iter<number_of_elements;iter++){/*minIndex denotes the index which has the minimum value which for now assumed to be the vlaue at current index and we update it in the for loop given below */ minIndex = iter;for(jter = iter+1; jter<number_of_elements;jter++){if(array[jter]< array[minIndex]){/* If some index has got element smaller than minimum then update minindex to be that index*/ minIndex = jter;}} temp = array[iter]; array[iter]= array[minIndex]; array[minIndex]= temp;}}int main(){int number_of_elements; scanf("%d",&number_of_elements);int array[number_of_elements];int iter;for(iter =0;iter < number_of_elements;iter++){ scanf("%d",&array[iter]);}/* Calling this functions sorts the array */SelectionSort(array,number_of_elements);for(iter =0;iter < number_of_elements;iter++){ printf("%d ",array[iter]);} printf("\n");return0;

MCQ Quiz: The Basics of Sorting Algorithms- Quadratic Sorts: Check how much you know about Quadratic Time Sorting Algorithms

MCQ Quiz #1: Quadratic Time Sorting Algorithms

One
of the most elementary sorting algorithms to implement - and also very
inefficient. Runs in quadratic time. A good starting point to understand
sorting in general, before moving on to more advanced techniques and
algorithms. A general idea of how the algorithm works and a the code for
a C program.

Another quadratic time sorting algorithm - an example
of dynamic programming. An explanation and step through of how the
algorithm works, as well as the source code for a C program which
performs insertion sort.

Another quadratic time sorting algorithm - an example
of a greedy algorithm. An explanation and step through of how the
algorithm works, as well as the source code for a C program which
performs selection sort.

In the average case, this works in O(n log n) time. No
additional memory overhead - so this is better than merge sort in this
regard. A partition element is selected, the array is restructured such
that all elements greater or less than the partition are on opposite
sides of the partition. These two parts of the array are then sorted
recursively.